Deprecate `skiprows=`, renaming it to `skiplines=` instead.

[seberg]

The skiprows option actually skips lines, so lets try make that explicit. A future step might be to actually add a skiprows (which ignores empty lines).

[seberg]

I think this should be handled in Python, so being lazy and assigning @rossbar :).

(Actually, a bit tricky if we want to support skiplines as positional parameter, but since it is hidden behind converters, I think that we can ignore that...)